Seasonal and diurnal photosynthetic responses of two gerbera cultivars to different substrates and heating systems

The simultaneous, long-term effects of three substrates (zeolite, perlite and their 1:1 mixture) and of two heating systems (lower and upper) upon the diurnal changes in photosynthesis of two gerbera cultivars (Cyprus and Heart Breaker) were investigated at different times of year. ‘Cyprus’ revealed higher net CO₂ assimilation rate and stomatal conductance than ‘Heart Breaker’, while transpiration rate was almost the same. Based on both stomatal conductance and transpiration rate, the zeolite–perlite mixture substrate exerted a more beneficial effect on the soil–plant water system. No change in chlorophyll levels, either time-wise or between gerbera cultivars, was observed in response to different substrates and heating systems. Diurnal net CO₂ assimilation rate, followed only for ‘Cyprus’, was reduced significantly from morning to late afternoon, possibly as a result of stomatal conductance reduction. The practical outcome with respect to the combined effect of different substrates, heating systems and cultivars was that ‘Cyprus’ grown on the mixture medium and subjected to an upper heating system (i.e. with heating pipes installed at the culture bag level) exhibited the best physiological responses.